Exposure time control system for photographic apparatus

ABSTRACT

Light is transmitted through the original onto photosensitive material in each of three primary colors. Three secondary electromultipliers furnish electrical currents which vary as a function of the light received by the photosensitive material in each color. Each current is integrated by a capacitor, the voltage on the capacitor compared to a reference voltage, and a relay energized when the capacitor voltage and the reference voltage have a predetermined relationship. Each relay has a first set of contacts for terminating the illumination in the corresponding color and a second set of contacts for shorting out part of a resistance connected in series between the supply voltage terminal and a transformer supplying voltage to the secondary electron multiplier corresponding to the other colors. This increases the sensitivity of the other electron multipliers, increasing the charging rate of the capacitor, and thus decreasing the exposure time in the other colors.

United States Patent [72] Inventors Gerhard Kuhn Leverkusen; Wolfgang Zahn; Walter Knapp, Munich, Germany [21 Appl. No. 769,868 [22] Filed Oct. 23, 1968 [45] Patented Apr. 27, 1971 [73] Assignee AGFA-Gevaert Aktiengesellschaft Leverlrusen, Germany [32] Priority Oct. 27, 1967 [33] Germany .l 1 91 078-2 [54] EXPOSURE TIME CONTROL SYSTEM FOR PHOTOGRAPHIC APPARATUS 12 Claims, 2 Drawing Figs.

[52] US. Cl 355/88, 355/36, 355/37, 355/38 [51] Int. Cl G031) 27/78 [50] FieldotSearch 355/36, 37,

38, 88, (inquired) [56] References Cited UNITED STATES PATENTS 3,100,419 8/1963 Clapp 355/38 3,293,033 12/ 1966 Maddock et a1. 355/38 Primary ExaminerSamuel S. Matthews Assistant Examiner-M. L. Gellner Attorney-Michael S. Striker ABSTRACT: Light is transmitted through the original onto photosensitive material in each of three primary colors. Three secondary electromultipliers furnish electrical currents whichvary as a function of the light received by the photosensitive material in each color. Each current is integrated by a capacitor, the voltage on the capacitor compared to a reference voltage, and a relay energized when the capacitor voltage and the reference voltage have a predetermined relationship. Each relay has a first set of contacts for terminating the illumination in the corresponding color and a second set of contacts for shorting out part of a resistance connected in series between the supply voltage terminal and a transformer supplying voltage to the secondary electron multiplier corresponding to the other colors. This increases the sensitivity of the other electron multipliers, increasing the charging rate of the capacitor, and thus decreasing the exposure time in the other colors.

PATENTEU m2 7 I97l Fig.2

INVENTOR. GERHARD KUHN WOLFGANG ZAHN WALTER KNAPP EXPOSURE TIME CONTROL SYSTEM FOR PHOTOGRAPIIIC APPARATUS BACKGROUND OF THE INVENTION This invention relates to a system for controlling the exposure time for different colors in photographic color copying equipment. In particular, it relates to control of exposure time in such a manner that undercorrection may be effected. In particular, it relates to such exposure control systems wherein photoelectric transducing means are used to evaluate the quantity of light falling on photosensitive material in each of three colors and wherein the illumination in each color is individually terminated when the corresponding quantity of light has reached a predetermined value.

As a rule in photographic reproducing equipment of the above-mentioned kind, the quantity of light falling on the photosensitive material in each color is so selected that the amount of light falling on the material for an even distribution over the surface of the material would cause a neutral gray to result after development. This so-called neutral gray compensation has the advantage that in the case of pictures lacking a very dominant color, a correct reproduction of the photographic scene results independent of possible color deviations in either the negative material or the photosensitive material. Furthermore, a color distribution whose sum results in a substantially neutral gray is particularly pleasing to the eye. To a certain extent a color copy may be considered adequate even if one color predominates slightly in the photograph scene, even though this color is not correctly reproduced. Only when a strong color dominant exists in the scene to be reproduced, that is when large surface areas of the scenehave the same color, do unsatisfactory color copies result from neutral gray compensation,

It is known that this defect in neutral graycompensation may be improved with so-called undercorrection. Thus differences in density of the, individual colors are only partly compensated for in determiningthe exposure time for each color.

SUMMARY OF THE INVENTION It is an object of the present invention to furnish an exposure control system of the above-mentioned type, wherein it is possible to effect undercorrection.

In particular, it is an object of this invention to furnish such a system which is particularly simple to combine with available photographic equipment having integrator type circuitry.

This invention comprises an exposure control arrangement having illuminating means for illuminating photosensitive material through an original in each of a predetermined plurality of colors, the illumination in a given color starting at an illumination starting time. It further comprises a plurality of measuring means corresponding in number to said plurality of colors, each for furnishing a color measurement signal corresponding to the total amount of light received by said photosensitive material in a corresponding color since the corresponding illumination starting time. Terminating means are 7 supplied for individually tenninating the exposure in said colors when the corresponding color measurement signal has reached a predetermined value. Further, exposure time changing means are provided for changing the exposure time for at least one color still being illuminated upon termination of the illumination in at least one other color.

The novel features whichare considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will now be described with reference to the FIGS.

In FIG. 1, reference numeral 1 denotes a supply voltage arrangement for secondary electron multipliers which serves to limit the usual sinusoidal supply voltage in both a positive and negative direction so that a substantially rectangular wave form is generated. The primary windings of three transformers which serve as a means for furnishing an applied voltage are connected to the voltage supply means 1 via a number of adjustment, compensation and calibration resistors. These primary windings arc the primary windings of transformers 2, 3, and 4, respectively. The corresponding secondary windings are each connected to photoelectric transducing means, here electron multipliers 5, 6 and 7. In particular, each secondary winding is connected between a cathode and one dynode of the corresponding secondary electron multipliers, while the anodes of all secondary electron multipliers are connected together to a source of positive potential, in this case stage 27.

The different resistances mentioned above will be described in detail. Directly connected to the means for furnishing a supply voltage, namely stage I, are resistance means denoted by reference numerals 8, 9 and 10. In this particular embodiment, resistance means comprise potentiometers. Potentiometers 8, 9 and 10 are each individually connected in parallel with normally open contacts 11a, 12a, 13a of relays ll, 12 and 13 to be described below. Connected in parallel to supply voltage source 1 is a voltage divider comprising a potentiometer l4 and a fixed resistor 15. The wiper arm of potentiometer 14 is connected to the series combination of three variable resistors l6, l7 and 18. These serve for density compensation. The wiper arms of resistors l6, l7 and 18 are coupled to further adjustable resistors 20 in each of the color channels in such a manner that a change in one color channel does not result in a change in total density of the copy. The operation of these resistors is disclosed in US. Pat. No. 3,355,984.

Three series resistance combinations each comprising a fixed resistor 21 and a potentiometer 19 as well as resistor 20 are connected between the other terminal of the series combination of resistors l6, l7 and 18 and the other supply voltage line. The primary of each transformer 2, 3, and 4 is connected to the variable arms of potentiometers 19 further adjustable resistor 20 in said series combination. A resistance 22 is connected in series to each primary winding.

The circuit associated with secondary electron multiplier 5 will now be discussed. The circuits for secondary electron multipliers 6 and 7 are analogous. The secondary electron multipliers with their associated circuits each comprise a color channel in which the light passing through the original and illuminating the photosensitive material in each of three prima ry colors is evaluated. The light for the secondary electron multipliers can be derived in a conventional fashion through a mirror arrangement in the path of the light and color separation by means of filters or, alternatively by means of dicroic mirrors. In either case, the light impinging on each secondary electron multiplier corresponds to light in one of three primary colors.

A capacitor 23 is connected to the dynode 9 of the secondary electron multiplier 5. The other terminal of the capacitor is connected to the secondary winding of transformer 2. This part of the secondary winding is also connected to ground via line 24. In parallel with the capacitor, a normally open relay contact 33 is controlled by a relay which is not shown. These contacts serve to discharge the capacitor at the end of a copying operation. The common point of dynode 9 and capacitor 23 is connected to the gate of an amplifier tube 25 which, in

conjunction with a further amplifier tube 26 present a high input impedance to the voltage on capacitor 23 and further, in conjunction with relay 11 serves as terminating means for this channel. The cathode of amplifier tube 25 is connected to means for furnishing reference voltage, namely stage 27 via resistors 29, 30, and 31. Stage 27 furnishes a reference voltage in accordance with the teachings of the German Pat. No. l,046,497, in which the exposure time and Schwarzschild effect of the photosensitive material are taken into consideration. Amplifier tube 26 allows current to flow through relay 11 via a direct current supply source 28. This relay in turn activates a normally open contact 11a which when closed short circuits the above-mentioned resistance 8. It further serves to activate another pair of contacts which in turn serves to terminate the illumination in thecorresponding color. For example these contacts may interrupt the current in a lamp or alternatively may serve to activate an electromagnet which pulls a subtractive filter into the path of the illumination, thus causing the illumination in the corresponding color to be terminated.

The operation of the above-described arrangement is as follows: Prior to the illumination starting time, all switches are in the position shown in FIG. 1. Relays 11, 12 and 13 are not activated and contact 11a, 12a, and 130 are therefore open. in this embodiment the illumination in all three colors start simultaneously and switches which short circuit capacitors 23 in all three channels are opened. The photocurrent generated by each of the secondary electron multipliers, which varies in correspondence to the color intensity in the original, are therefore integrated in the capacitors 23 causing the voltage on each capacitor to increase. The voltage on this capacitor constitutes the color measurement signal. The increase in voltage of the capacitors is a function not only of the light intensity at the photo cathode of the secondary electron multiplier, but also depends on the voltage in the circuit of the primary winding of each of the transformers 2, 3, and 4. Potentiometers 8, 9 and effect all three of these voltages simultaneously as do potentiometers 16, 17 and 18. The operation of these potentiometers or variable resistors is as follows: The wiper arms of the potentiometers 16, 17 and 18 are so coupled with the wiper arms of variable resistors 20 which effect each applied voltage separately in such a manner that a change in the sensitivity in the color channel comprising secondary electron multiplier 5 causes no change in the total density of the copy since the sensitivity of the other two channels is changed in the opposite direction. Potentiometers 19 and 22 serve for individual adjustment of each color channel, for example potentiometer 19 may be used for calibration of the equipment, while potentiometer 22 may be adjusted to compensate for the particular characteristics of the corresponding secondary electron multiplier.

The voltage on capacitor 23 thus increases in correspondence to the voltage applied to the photosensitive transducing means, that is the voltage across the secondary winding of each transfer which in turn is determined by the voltage on the primary winding of each transformer. It is further, of course, a function of the illumination reaching the corresponding secondary electron multiplier 5, 6 and 7. Amplifier tubes 25 and 26 serves to compare this capacitor voltage to a reference voltage supplied by stage 27. This reference voltage has a value which takes into consideration the Schwarzschild effect and other characteristics of photosensitive material. When a predetermined relationship is reached between the voltage on the capacitor and said reference voltage, the corresponding relay 11, 12 and 13 is energized. Energization of a relay on the one hand causes immediate temiination of illumination in the corresponding color. As mentioned above, this may be accomplished by inserting a subtractive filter into the path of the illumination. Alternatively, it might be accomplished by opening normally closed contacts in a lamp. The latter method is appropriate when the photographic apparatus has a different lamp serving as a source of illumination for each color.

Energization of the relay, for example relay 11, also causes a closing of normally open contact pair 11a which short circuits potentiometer 8. In this way the resistance in the primary circuit of transformers 3 and 4 is decreased causing the voltage applied to secondary electron multipliers 6 and 7 to be increased, which in turn causes an increase in the rate of change of voltage on the corresponding capacitors. This is illustrated in FIG. 2 which shows a plot of the capacitor voltage on each capacitor starting with the illumination starting time at t=0. The charging voltage of capacitor 23 associated with secondary electron multiplier 5 is denoted by R while the charging voltages on the other two capacitors are denoted by G and B. it will be noted that the rate of change of voltage on these capacitors remains constant from the time i=0 until the illumination is terminated in the R channel. At this point due to the shorting of resistance 8 the rate of change of voltage in the G and B channels increase. Upon termination of the illumination of the G channel it will be noted that the rate of change of voltage on the capacitor in the B channel again increases. This is caused by the shorting of resistance 9 caused by the closing of relay contacts 12a upon energization of relay 12. Thus the exposure time for colors remaining after termination of illumination in one channel is shortened due to the increase in voltage rate of change on capacitors remaining after termination of illumination in the other channels.

This arrangement has the particular advantage that special circuits as for example reference voltage generator 27 which may be varied in accordance with the Schwarzschild effect may continue to serve their function as prior to the use of circuitry as disclosed herein. Adjustment of the various potentiometers such as potentiometer 16, 17, 18, 19 and 20 in the primary circuit of the transformer is also not effected by this undercorrection arrangement.

Since the embodiment of resistance means 8, 9 and 10 shown in the FIG. comprise potentiometers, the possibility exists to effect a separate undercorrection for each color. However, other means are available for such a separate undercorrection and it is therefore desirable to mechanically intercouple all three variable arms on a single shaft. Then a single adjustment may be made for the desired degree of undercor' rection.

It is, of course, also possible to use groups of fixed resistors instead of potentiometers 8, 9 and 10. in this case a single step switch may be used to effect the desired undercorrection.

While the invention has been illustrated and described as embodied in particular circuit configuration, it is not intended to be limited to the details shown, since various modification and circuit changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

We claim:

1. In an apparatus for producing color copies of a color original on photosensitive material; an exposure control arrangement, comprising in combination, illuminating means for illuminating said photosensitive material through said original in each of a predetermined plurality of colors, the illumination in a color starting at a corresponding illumination starting time; a plurality of measuring means corresponding in number to said plurality of colors, each for furnishing, subsequent to the corresponding illumination starting time, a color measurement signal corresponding to the total amount of light having illuminated said photosensitive material in the corresponding color since the corresponding illumination starting time; terminating means for individually terminating the exposure in each of said colors when the corresponding color measurement signal has reached a predetermined value; and exposure time changing means for changing the exposure time for at least one color still being illuminated upon termination of the illumination in at least one other color.

2. An exposure control arrangement as set forth in claim 1 wherein said plurality of colors comprises three colors.

3. An exposure control arrangement as set forth in claim 2 wherein said exposure time changing means comprise means for shortening the exposure time for at least one color still being illuminated upon termination of the illumination in at least one other color.

4. An exposure control arrangement as set forth in claim 3 wherein said measuring means comprise photoelectric transducing means for generating three electrical signals, each varying as a function of the amount of light illuminating said photosensitive material in a corresponding one of said colors; and electrical integrator means for integrating each of said electrical signals thus furnishing said color measurement signals.

5. An exposure control arrangement as set forth in claim 4 wherein said electrical integrator means comprise capacitors; and wherein said electrical signals comprise the charging currents for said capacitors.

6. An exposure control arrangement as set forth in claim 5 wherein said photoelectric transducing means comprise a plurality of photoelectric transducing means, one for each of said colors; wherein said charging currents also vary as a function of voltage applied to the corresponding photoelectric transducing means; and wherein said exposure time changing means comprise means for changing said applied voltage of at least one other of said photoelectric transducing means upon termination of illumination in any one color.

7. An exposure control arrangement as set forth in claim 6 wherein said terminating means comprise a plurality of relay means, one for each of said colors; and energizing means, one for each of said relay means, for energizing the corresponding relay means when the voltage on the corresponding capacitor has reached a predetermined value.

8. An exposure control arrangement as set forth in claim 7 further comprising means for furnishing a reference voltage; and wherein said energizing means comprise electronic switching means connected to said means for furnishing a reference voltage, to the corresponding capacitor, and to the corresponding relay means in such a manner that said relay means are energized when the corresponding capacitor voltage has reached a predetermined relationship to said reference voltage.

9. An exposure control system as set forth in claim 8 further comprising voltage supply means to furnish a supply voltage; and resistance means, sen'es connected between said voltage supply means and said photoelectric transducing means; and wherein said means for changing said applied voltage comprise means for short circuiting a predetermined corresponding part of said resistance means upon termination of the illumination in each of said color.

10. An exposure control system as set forth in claim 9 wherein said means for short circuiting a predetermined part of said resistance means comprise three pairs of normally opened relay contacts, one pair associated with each of said relay means.

11. An exposure control system as set forth in claim 10 wherein said predetermined parts of said resistance means each comprise a potentiometer having a wiper arm; and wherein all of said wiper arms are mechanically intercoupled.

12. An exposure control system as set forth in claim 10, wherein each of said predetermined parts of said resistance means comprises a fixed resistor; further comprising additional resistors for each of said parts; and means for selecting difi'erent ones of said additional resistors to constitute said of undercorrection. 

1. In an apparatus for producing color copies of a color original on photosensitive material; an exposure control arrangement, comprising in combination, illuminating means for illuminating said photosensitive material through said original in each of a predetermined plurality of colors, the illumination in a color starting at a corresponding illumination starting time; a plurality of measuring means corresponding in number to said plurality of colors, each for furnishing, subsequent to the corresponding illumination starting time, a color measurement signal corresponding to the total amount of light having illuminated said photosensitive material in the corresponding color since the corresponding illumination starting time; terminating means for individually terminating the exposure in each of said colors when the corresponding color measurement signal has reached a predetermined value; and exposure time changing means for changing the exposure time for at least one color still being illuminated upon termination of the illumination in at least one other color.
 2. An exposure control arrangement as set forth in claim 1 wherein said plurality of colors comprises three colors.
 3. An exposure control arrangement as set forth in claim 2 wherein said exposure time changing means comprise means for shortening the exposure time for at least one color still being illuminated upon termination of the illumination in at least one other color.
 4. An exposure control arrangement as set forth in claim 3 wherein said measuring means comprise photoelectric transducing means for generating three electrical signals, each varying as a function of the amount of light illuminating said photosensitive material in a corresponding one of said colors; and electrical integrator means for integrating each of said electrical signals thus furnishing said color measurement signals.
 5. An exposure control arrangement as set forth in claim 4 wherein said electrical integrator means comprise capacitors; and wherein said electrical signals comprise the charging currents for said capacitors.
 6. An exposure control arrangement as set forth in claim 5 wherein said photoelectric transducing means comprise a plurality of photoelectric transducing means, one for each of said colors; wherein said charging currents also vary as a function of voltage applied to the corresponding photoelectric transducing means; and wherein said exposure time changing means comprise means for changing said applied voltage of at least one other of said photoelectric tRansducing means upon termination of illumination in any one color.
 7. An exposure control arrangement as set forth in claim 6 wherein said terminating means comprise a plurality of relay means, one for each of said colors; and energizing means, one for each of said relay means, for energizing the corresponding relay means when the voltage on the corresponding capacitor has reached a predetermined value.
 8. An exposure control arrangement as set forth in claim 7 further comprising means for furnishing a reference voltage; and wherein said energizing means comprise electronic switching means connected to said means for furnishing a reference voltage, to the corresponding capacitor, and to the corresponding relay means in such a manner that said relay means are energized when the corresponding capacitor voltage has reached a predetermined relationship to said reference voltage.
 9. An exposure control system as set forth in claim 8 further comprising voltage supply means to furnish a supply voltage; and resistance means, series connected between said voltage supply means and said photoelectric transducing means; and wherein said means for changing said applied voltage comprise means for short circuiting a predetermined corresponding part of said resistance means upon termination of the illumination in each of said color.
 10. An exposure control system as set forth in claim 9 wherein said means for short circuiting a predetermined part of said resistance means comprise three pairs of normally opened relay contacts, one pair associated with each of said relay means.
 11. An exposure control system as set forth in claim 10 wherein said predetermined parts of said resistance means each comprise a potentiometer having a wiper arm; and wherein all of said wiper arms are mechanically intercoupled.
 12. An exposure control system as set forth in claim 10, wherein each of said predetermined parts of said resistance means comprises a fixed resistor; further comprising additional resistors for each of said parts; and means for selecting different ones of said additional resistors to constitute said predetermined parts, in dependence upon the desired degree of undercorrection. 